It's an odd switch not logical. If It's off there will be no light on (store) if you plug the power cord in it should light up even without moving the switch. You can use everything in the camper at this point. Now if you want to send power to the battery for charging you will need to push the button to use you will hear a sound as you push button now the converter/charger is sending power to the battery. You can check this with a voltmeter at the battery posts. Before and after pushing the use button. If you are not plugged in and want to use the
12 volt systems You will need to push the button to use the light will come on. The converter/charger that comes standard in AS's is poor in that it only sends a single voltage to battery and takes a long time to charge and can over charge if left on too long. I changed mine to a progressive dynamics PD4655 a three stage charger an easy up grade and works well. Good camping Rand